When an energy-storing phosphor (e.g., stimulable phosphor, which produces stimulated emission) exposed to radiation such as X-rays, it absorbs and stores a portion of the radiation energy. The phosphor then emits stimulated emission according to the level of the stored energy when it is exposed to electromagnetic wave such as visible or infrared light (i.e., stimulating light). A radiation image recording and reproducing method utilizing the energy-storing phosphor has been widely employed in practice. In that method, a radiation image storage panel, which is a sheet comprising the energy-storing phosphor, is used. The method comprises the steps of: exposing the storage panel to radiation having passed through an object or having radiated from an object, so that radiation image information of the object is temporarily recorded in the storage panel; sequentially scanning the storage panel with a stimulating light such as a laser beam to emit a stimulated light; and photoelectrically detecting the emitted light to obtain electric image signals. The storage panel thus treated is subjected to a step for erasing radiation energy remaining therein, and then stored for the use in the next recording and reproducing procedure. Thus, the radiation image storage panel can be repeatedly used.
The radiation image storage panel (often referred to as energy-storing phosphor sheet) has a basic structure comprising a support and an energy-storing phosphor layer provided thereon. However, if the phosphor layer is self-supporting, the support may be omitted. Further, a protective layer is ordinarily provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical damage.
The phosphor layer usually comprises a binder and an energy-storing phosphor dispersed therein. However, the phosphor layer may comprise agglomerate of an energy-storing phosphor without binder. The phosphor layer containing no binder can be formed by a vapor phase deposition procedure or by a firing procedure. Further, the phosphor layer may comprise energy-storing phosphor agglomerate impregnated with a polymer material.
Japanese Patent Provisional Publication 2001-255610 discloses a variation of the radiation image recording and reproducing method. While an energy-storing phosphor of the storage panel used in the ordinary method plays both roles of radiation-absorbing function and energy-storing function, those two functions are separated in the disclosed method. In the method, a radiation image storage panel comprising an energy-storing phosphor (which stores radiation energy) is used in combination with a phosphor screen comprising another phosphor which absorbs radiation and emits ultraviolet or visible light. The disclosed method comprises the steps of causing the radiation-absorbing phosphor of the screen (and of the storage panel) to absorb and convert radiation having passed through an object or having radiated from an object into ultraviolet or visible light; causing the energy-storing phosphor of the storage panel to store the energy of the converted light as radiation image information; sequentially exciting the energy-storing phosphor with a stimulating light to emit stimulated light; and photoelectrically detecting the emitted light to obtain electric signals giving a visible radiation image.
The radiation image recording and reproducing method (or radiation image forming method) has various advantages as described above. However, it is still desired that the radiation image storage panel used in the method show as high sensitivity as possible and, at the same time, give a reproduced radiation image of high quality (particularly, in regard to sharpness and graininess).
In reading out radiation image information from the radiation image storage panel, line-scanning is often adopted. The system of line-scanning ordinarily comprises a condenser lens (e.g., distributed index lens array) and a line sensor in combination. Light emitted from the storage panel is focused through the condenser lens onto a photo-receiving face of the line sensor, and the line sensor detects and photoelectrically converts the emission into electric signals. Accordingly, it is important to prevent the storage panel from bending and to keep the storage panel such level that the distance between the lens and the panel surface is kept within the depth of focus. In consideration of these requirements, it has been proposed to provide a rigid plate or support onto one or both sides of the phosphor layer.
Meanwhile, in producing the radiation image storage panel, an energy-storing phosphor layer and a protective layer are often formed on a continuous support, and then other steps such as a step of cutting, a step of placing other sheets or layers and/or a step of attaching a rigid plate are carried out. It is now found that if these post-treatment steps are carried out without covering or protecting the phosphor and protective layers, the surface of the phosphor or protective layer (namely, the panel surface on the side from which the image information is read out) is often scratched or bruised because the layers are locally rubbed or pressed when handled or treated in the above steps. As a result, the reproduced radiation image obtained in the radiation image storing and reproducing procedure is often impaired. Further, the surface is also bruised by dust (such as waste fragments of the phosphor) attaching thereonto.
Furthermore, the manufactured storage panel may be rubbed or scratched when packed, transported or stored, so the surface of the storage panel may be damaged. In addition, when the storage panel is installed in a built-in type radiation image information recording and reproducing apparatus (which is equipped with a built-in panel), the surface of the storage panel is, if not protected, often damaged during the installation.